This download looks like a save. You need to place it in your saves folder inside the Garry's Mod folder.
You should end up with a directory structure similar to below:
Don't know where the Garry's Mod folder is or how to extract zip files? See more useful installation tips.
ponl1234, Tekno Rage Gamez, Shadow, chooramun.sanjiv, ︻芫══--- d1fficult ッ, Hashtag Hasagi, Hashtag Hasagi, yusal_i, Neplo 998, Doctor Zebra, TheMarcMaverick, [XOG]Jakey]JTB]ST], [XOG]Jakey]JTB]ST], zShock1224, Ðiablo